Device for varying the stability of marine craft



June 1 c. VON DEN STEINEN 2,352,044

DEVICE FOR VARYING THE STABILITY OF MARINE CRAFT Filed Opt. 16, 1940' Patented June 20, 1944 DEVICE FOR- VARYING THE STABILITY OF MARINE CRAFT Carl von den Steinen, Hamburg, Germany; vested in the Alien Property Custodian Application October 16, 1940, Serial No. 361,463 In Germany November 22, 1939 1 Claim.

The invention relates to a device for influencing-particularly for reducingthe initial stability of marine craft. The initial stability of a ship, being designed to withstand the most unfavorable meteorological and nautical conditions, is not favorably suited for medium or smooth seas because the motions of the ship, according to the respective conditions of resonance, may be unpleasantly felt when medium or smooth seas are encountered. The greater the initial stability, that is to say the greater the metacentri-c height of the ship, the shorter is the period of the rolling motion of the ship hence, the shorter, sharper and harder, the sensation produced by such motion. It is therefore the endeavor of ship constructors to find a device bywhich the values of the initial stability and therefore the rolling period of the vessel may be influenced.

It is already known that the initial stability of ships may be reduced by means of freely movable liquid masses. Tanks used for this purpose are called stability reducing tanks. As soon, however, as a vessel, provided with such partly filled tanks, starts to roll, the liquid in the tanks starts rolling likewise. This results in a relative displacement of the phases of the motions of the ship and of the motions of the tank water which in a state of resonance reach the amount of 90".

Such a tank operates dynamically and has become similar to a Frahm rolling tank. In order to meet this emergency it has been proposed to provide dampening partitions in the tank, but although dampening reduces this efiect, a certain phase displacement remains.

According to other proposals, devices operated either manually or automatically are provided for synchronizing the motional' phases of the liquid and of the rolling of the ship. In these proposals, the rolling of the ship is referred to the vertical (true vertical) relative to which the vertical axis of the vessel assumes different oblique positions (rolling angle). The synchronization of the phases according to this reference system cannot lead to a favorable solution because the system is based on conditions prevailing only when the vessel is artificially rolled in a calm sea and at a horizontal water surface. In the open sea, however, when the waves act on the body of the ship the conditions are essentially different.

The present invention particularly aims at improving the so-called stability reducing tanks in the sense referred to and has as an object a novel construction which lacks many of the disadvantages in devices of the prior art.

a system for limiting the rolling of a ship by the use of interconnected water tanks, one on each sideof the ship, and means for driving water into either tank.

A further object of the invention is to provide a, construction of this class in which two tanks are connected by a conduit that contains means, operated in accordance with the rolling of the ship, to drive water from the conduit into either of the tanks and that is also provided with means for closing thhe conduit and rendering the system inoperative.

To these ends and for the purpose of more fully explaining the invention, there is shown in the accompanying drawing one means for carrying the same into practical effect- The single view in the drawin is a schematic cross section taken transversely through the hull of a ship which is provided with the system and device forming the subject of this invention. 7

In carrying out the invention two short pendulums are employed. One pendulum is carried by the other and the'last named pendulum is suspended on an axis which is fixed with respect to the ship and which runs longitudinally thereof. The carried pendulum is freely movable and hence seeks to adjust itself in the direction of the apparent vertical. On the other hand, means are provided for urging the other pendulum, that is to say the one suspended from the fixed axis, in a direction opposed to the apparent vertical. The apparent vertical pendulum suspended on the fixed axis will hereinafter be termed the operative apparent vertical pendulum-because it is mechanically moved relative to the ship while the pendulum carried by it is not so urged being freely movable and will be called the non-operative apparent vertical pendulum. The point of suspension of the non-operative apparent vertical pendulum is located above the center of oscillation of the operative apparent vertical pendulum by a distance equal to the length of the former.

A well-balanced freely swinging pendulum suitably located within the hull of the ship serves to dampen the rolling movement, i. e. it has a stabilizing effect. The center of gravity of the liquid masses of the previously mentioned Frahm anti rolling tank moves in accordance with the mass of the freely swinging pendulum. Thus the Frahm anti-rolling tank and the freely swinging pendulum are equivalent swinging systems. The short operative apparent vertical pendulum is based on quite a diiierent principle. Such a Another object of the invention is to provide 5 pendulum counteracts the stability, 1. e. it reline which is at the same time vertical to the Any moved mass may be regarded as an equivalent system to the apparent vertical pendulum;

provided said mass is moved in accordance with the movement of the apparent vertical pendulum, i. e. that the velocity of the movement of the center of gravity is phaselessly proportional to the angular velocity of the apparent vertical. Such a system may also be characterized as having an imaginary point of suspension the line connecting such point with the center of gravity of the masses always running in the direction of the straight line of the apparent vertical. A system in which a suitable point of suspension" of a movable mass has been found which together with the center of gravity determines a straight line running in the direction of the apparent vertical, is the equivalent of the operative apparent vertical pendulum system. Such a system more particularly is one in which a mass of constant geometrical formmoves rhythmically along a straight line lying transverse to the longitudinal axis of the ship.

Another system equivalent to the apparent vertical pendulous system consists in an activated rolling tank in which the movement of the liquid is controlled in a certain manner and in such a way that the center of gravity of the liquid masses executes the movement of an apparent vertical pendulum. Thus the pendulum must move in such a way that a line connecting the center of gravity with a certain predetermined imaginary suspension point (tank water metacenter) points in the direction of the apparent vertical.

A tank system equivalent to the operative apparent'vertical pendulum is in the following described as a static tank in distinction from the dynamic tank which is equivalent to a freely swinging pendulum and in which the center of gravity of the liquid therefore moves in the same manner as the freely swinging pendulum. It now becomes apparent why, as already mentioned, the solution by means of stabilityreducing tanks with dampening partitions only represents a part solution, as such dampened tanks correspond'to a dampened freely swinging pendulum. Such a tank therefore is something between a dynamic and a static tank whilst in accordance with the invention only static tanks can serve to successfully reduce the initial stability.

It follows from the foregoing that any antirolling tank serving for stabilizing purposes on account of the freely movable liquid masses swinging about the longitudinal axis of the vessel may be used as stability reducing tank by suitably controlling the liquid movement in dependence on the movements of an apparent vertical. In such a controlling arrangement particular care must be taken that the liquid movement is in entire synchronism with the velocity of the apparent vertical so that both movements always simultaneously pass the zero position determined by the vertical axis of the ship. Such control may be effected by means of an apparent vertical.

In addition, the amplitude of the liquid movelongitudinal axis of the ship. The angle formed by this vertical with the vertical axis of the ship may be designated by 1,0 and the angle formed by an apparent vertical pendulumfor instance a non-operative one-swinging in a plane vertical to the ships longitudinal axis, and the ships vertical axis being designated by o. Now the tank is an operative apparent vertical pendulum if in which k stands for a positive constant. This equation is so characteristic that it might define a pendulous mass system equivalent to an operative apparent vertical pendulum instead of introducing an imaginary suspension point. In order to maintain the proportionality between (p and ,0 the tank is also activated in response to the amplitude of an apparent vertical as controlling element, as the constant k is also determined by the ratio between the apparent vertical amplitude and the tank water amplitude. A mode of control permitting also the variation of the constant k may be termed transmission control. By means of such transmission control it is possible to influence the amplitude, or, what amounts to the same, the velocity of the tank water movement in order to suitably adjust the amount of reduction of the initial stability.

The case of Ic=1 deserves particular attention.

Here the effective tank water level always swings with the apparent vertical horizon. At this so called normal transmission, the tank water level (the line between the centers of gravity of the tank water levels in the two tanks) will adjust itself parallel to the effective wave slope, i. e. in the apparent vertical horizon. In such case only a pump will be required for moving the tank water. As the pump in this instance needs only to overcome the friction between the liquid and thetank walls, particularly in the overflow channel, and also the inertia of the tank water relative to the horizon, it will be required to deliver only a relatively small force. No actual action of lifting quantities of water or the like is required in. this connection. This will be necessary, however, if the effectiveness is to be enhanced or weakened by artificially decreasing or increasing the amplitude of motion (variation of the transmission ratio). In this case the control is likewise effected with reference to an apparent vertical, while a different proportional constant between the apparent vertical and the velocity of the tank water movement is obtained as compared with the normal transmission.

With particular reference to the drawing, the stability reducing tank in the hull 3 is, according to the invention, of a U shape. The tank consists of two leg portions l and I connected together by a water overflow channel 2 and an air overflow channel 2'.

A propeller 4 in the channel 2 serves to effect the movement of the liquid in the tank, this propeller being driven by an electric motor 6. A short apparent vertical pendulum 13, which corresponds to the non-operative apparent vertical pendulum heretofore referred to, is suspended from the axis I on an adjusting segment I4. The adjusting segment I4 corresponds to the short operating apparent vertical pendulum previously mentioned. Segment I4 is pivoted on an axis I5 which runs longitudinally of the ship, this axis being maintained in fixed position with respect to the ship. It may also be noted that the axis I5 of the pendulum l3 also extends longitudinally of the vessel but moves in accordance with the swinging action of the segment I 4.

Pendulum i3, is restrained within narrow limits relative to the segment I4 by means of stops I9 and carried on the latter. As already mentioned the segment I4 is swingably mounted about the axis I5, this axis extending parallel to the axis I5 and being about level with the swinging center of the pendulum I3. Means for moving the segment I4 about its pivot include a plurality of teeth formed on its lower periphery and engaged with a worm wheel I4 driven by an electric motor I8. The motor I8 is controlled by means of the contacts I9 and 20 and pendulum I3 in such manner that the motor adjusts the segment I4 so that the pendulum I3 is freely suspended between the contacts in the direction of the gravitational force. 'A ratio slider 26 with two levers I6 and I1 is connected to the segment l4. Movement of the segment I4 is transmitted to this slider 26 and in turn is imparted to a synchronizing device I, which latter derives a control impulse from the impulse received from the apparent vertical, to the end of correctly controlling the operation of the tank propeller 4. The latter must operate at an angular velocity proportional to the angular velocity of the axle of the worm wheel I l. The controlling impulse is conducted to a well lmown jet pipe relay 8 and 9 by means of levers II and I2, said relay displacing a tap in the resistance ID in the circuit of the motor 6. If the synchronizing device is suitably constructed, the motor 6 by means of the propeller 4 sets the tank liquid into the desired motion. The synchronizing device 1 is primarily designed to establish synchronism between the movements derived from the apparent vertical and the movements of the tank water and especially to maintain such synchronism even in the face of variations of transmission. It may in addition serve to suitably utilize the amplitude of the apparent vertical movement for the control of the tank water. This latter may also be achieved by means of the ratio slider 26 which effects a variable transmission between the apparent vertical and the jet pipe relay. Thus, the amplitude of the apparent vertical movement may be likewise utilized by displacement of the ratio slider. Instead of the jet pipe relay any kind of relay may of course be used.

In accordance with the invention, the control of the tank liquid in dependence on the amplitude of the apparent vertical may also be restricted to a certain angular range to be adjusted according to the circumstances. In this instance, the stability of the ship is. reduced only until its movements exceed the apparent vertical rolling angle. When the latter is the case, the tank switches itself ofi automatically. Now if the weather conditions or the loading conditions of the ship should call for an increase even of the initial stability,

it is possible, either over the whole angular range or beginning from a certain set predetermined rolling angle, by means of the ratio slider 26 to cause the tank water to swing synchronously in opposition to the wave slope. Accordingly, the constant is becomes a negative value. Through this swinging motion, the efiective center of gravity of the ship is lowered whereby the effectiveness of the initial stability is enhanced. Finally a quick closing valve, manually or automatically operated, may be arranged in one of the overflow channels for switching on the tank, i. e. for rendering it inoperative. Such a valve, which may also be termed an emergency brake, is indicated in the drawing by the numeral 5. Although here the increase of the initial stability of the ship is only considered in connection with the stability reducing device, it may represent an important feature in itself.

Instead of an ordinary tank one may use a tank consisting of two separate containers located in the bow and stem, respectively, each of such containers communicating with the water via orifices in the hull of the ship. A stability reducing efiect may likewise be obtained by such tanks by alternately flooding and draining, provided this is done in a certain dependence on the apparent vertical movements.

What I claim is:

The combination in a ship of a system for stabilizing the ship comprising tanks located on opposite sides of the ship, conduit means connecting said tanks in communication with each other, said tanks and said conduit containing water, impeller means comprising blade members rotatably mounted within said conduit for causing water within said conduit to be driven into either tank inaccordance with the directions of rotation of said impeller means, drive means for rotating said impeller means in a desired direction, means responsive to lateral inclinations of the ship and operatively connected to said drive means to cause actuation thereof whereby upon a lateral inclination of the ship in one direction the impeller means are operated to drive water in the conduit means into the tank on the side of the ship which is rolling upwardly and upon lateral movement of the ship in the opposite direction the impeller means are operated to drive water in the conduit means into the second tank, and valve means within said conduit means for closmg the conduit and rendering the stabilizing system inoperative.

CARL VON DEN STEINEN. 

